Motor control system

ABSTRACT

An inverter part having a switching unit for applying a three-phase AC voltage to a motor, a lock detection unit for detecting a lock state of the motor and also generating a lock detection signal by the detection, and a current control unit for passing a d-shaft armature current id through the motor so that an absolute value of a current of a phase with the largest current flowing through the motor decreases based on the lock detection signal.

TECHNICAL FIELD

The present invention relates to a motor control system, and extends alife of an inverter part by passing a d-shaft armature current through amotor at the time of a lock of the motor.

BACKGROUND ART

In a motor control system disclosed in JP-A-9-121595, a technique inwhich when it is detected-that a temperature of a switching elementforming an inverter part increases, a frequency (hereinafter called acarrier frequency) of a carrier signal of a PWM circuit is firstdecreased and when the temperature increases still, control is performedso as to decrease torque of a motor and an increase in temperature ofthe inverter part is prevented is disclosed.

On the other hand, in a motor-driven injection molding machine, thepractice of periodically opening and closing a movable metal mold drivenby a motor with respect to a fixed metal mold is made. In such openingand closing, at the time of closing, the movable metal mold and thefixed metal mold are pressed and the motor becomes a lock state and atthe time of opening, the movable metal mold moves and thereby the motorbecomes an operation state. That is, the motor repeats the operation andlock states periodically.

In the case that a motor is in the lock state, as described inJP-A-6-38544, a magnitude and a direction of a current flowing througheach phase of the motor are fixed, so that a large current flows throughone particular switching element forming an inverter part. Therefore, atemperature of the one switching element increases extremely than thatof the other switching element.

In such a use, as described in JP-A-9-121595, when the carrier frequencyor the torque is decreased after detecting that the temperature of theswitching element forming the inverter part increases, there was aproblem that power loss of all the switching elements decreasesuniformly and it is not efficient and variations in power loss occurringin each the switching element are large.

In addition, when the carrier frequency is decreased, a ripple currentof the motor increases and noise generated from the motor increases.When the torque is decreased, there was a problem that torque generatedfrom the motor becomes improper with respect to a drive load.

The present invention is implemented to solve the problems, and anobject of the invention is to provide a motor control system for makingpower loss of each switching element of an inverter part as uniform aspossible by passing a d-shaft armature current i_(d) through a motor atthe time of a lock in a use in which the motor is locked.

DISCLOSURE OF THE INVENTION

A motor control system according to a first invention is characterizedby comprising an inverter part having switching means for applying athree-phase AC voltage to a motor, lock detection means for detecting alock state of the motor and also generating a lock detection signal bythe detection, and current control means for passing a d-shaft armaturecurrent i_(d) through the motor so that an absolute value of a currentof a phase with the largest current flowing through the motor decreasesbased on the lock detection signal.

According to such a motor control system, the current control meanspasses a d-shaft armature current i_(d) through the motor so as todecrease an absolute value of a current of a phase with the largestcurrent flowing through the motor by the lock detection signal.Therefore, even in the case that the motor is in the lock state, thereis an effect capable of suppressing noise generated from the motorwithout remarkably shortening a life of the particular switching meansforming the inverter part.

In the first invention, it is characterized in that the current controlmeans of a motor control system according to a second invention passes ad-shaft armature current i_(d) through the motor so that absolute valuesof currents of two phases are larger than that of the other one phaseamong three phases whose the currents flow through the motor are madesubstantially equal.

According to such a motor control system, the current control meanspasses a d-shaft armature current through the motor so that absolutevalues of currents of two phases are larger than that of the other onephase among three phases whose the currents flow through the motor aremade substantially equal and thereby, even in the case that the motor isin the lock state, a large current does not flow through a particularphase of the motor furthermore. Therefore, there is an effect that alife of the particular switching means forming the inverter part is notshortened furthermore.

In the first or second invention, it is characterized in that thecurrent control means of a motor control system according to a thirdinvention satisfies the following A when it is assumed that a q-shaftarmature current passed through the motor is I_(q) and a magnetic poleposition of the motor is θ_(r).I_(d)=AI_(q)

-   -   where A=tan (θ_(r)−π·n/3)    -   n=0 for 0°<θ_(r)≦30°, 330°<θ_(r)≦360°,    -   n=1 for 0°<θ_(r)≦90°, n=2 for 90°<θ_(r)≦150°,    -   n=3 for 150°<θ_(r)≦210°, n=4 for 210°<θ_(r)≦270°,    -   n=5 for 270°<θ_(r)≦330°

According to such a motor control system, the current control meanspasses a d-shaft armature current i_(d) so as to satisfy the above A, sothat an angle at which a magnetic pole position of the motor is shiftedequivalently becomes a maximum of 30°. Therefore, the necessary d-shaftarmature current i_(d) to be passed through the motor can be suppressed,so that there is an effect capable of suppressing the maximum value of acurrent flowing through each phase of the motor.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front view applying a motor control system according to oneembodiment of the present invention to a motor-driven injection moldingmachine.

FIG. 2 is the entire configuration diagram of the motor control systemaccording to one embodiment.

FIG. 3 is a current waveform chart flowing through each phase of a motorshown in FIG. 1.

FIG. 4 is a flowchart showing an action of the motor control systemshown in FIG. 1.

BEST MODE FOR CARRYING OUT THE INVENTION

First Embodiment

Next, a motor control system according to one embodiment of the presentinvention will be described by FIGS. 1 to 3. FIG. 1 is a front viewapplying the motor control system according to one embodiment to amotor-driven injection molding machine, and FIG. 2 is the entireconfiguration diagram of the motor control system shown in FIG. 1, andFIG. 3 is a current waveform chart flowing through each phase of a motorshown in FIG. 1.

In FIG. 1, a metal mold opening and closing apparatus 1 of themotor-driven injection molding machine comprises a nut 7 mounted in anend plate 9 while being screwed to a screw shaft 5 rotated by rotationof a three-phase permanent magnet synchronous type motor (hereinaftercalled a motor) 3 driven and controlled by a controller, a movable metalmold 13 fixed through a movable platen 11 fixed in the top of the screwshaft 5, a fixed metal mold 15 fixed in a fixed platen 14, and bars 17for guiding the movable platen 11 while being fixed in the end plate 9and the fixed platen 14, and an encoder 40 for detecting a rotationalangle is provided in a shaft of the motor 3, and it is constructed sothat detection parts of Hall element type current sensors 45 u, 45 v, 45w detect currents flowing through a U phase, a V phase, a W phase of themotor 3 by extending through output lines of a controller 20.

The controller 20 comprises a DC power source part 25 for converting anAC power source into a DC power source, a three-phase inverter part 30for converting a DC voltage of the DC power source part 25 into an ACvoltage of a variable voltage variable frequency and also driving themotor 3, a control part 50 for driving the inverter part 30 based ondetection values of the current sensors 45 u, 45 v, 45 w, and a drivingpart 70 for amplifying an output of the control part 50.

The DC power source part 25 comprises a converter 27 for converting athree-phase AC voltage into a DC voltage and a capacitor 29 forsmoothing a ripple of the DC voltage, and the inverter part 30 comprisestransistors T₁, T₂, T₃ forming upper side U phase, V phase, W phaseacting as switching means provided in the upper side, transistors T₄,T₅, T₆ forming lower side U phase, V phase, W phase acting as switchingmeans provided in the lower side, diodes D₁, D₂, D₃ respectivelyconnected in parallel with the transistors T₁, T₂, T₃, and diodes D₄,D₅, D₆ respectively connected in parallel with the transistors T₄, T₅,T₆.

An input I/F 52 for capturing detection values of the encoder 40 and thecurrent sensors 45 u, 45 v, 45 w, a CPU 54, ROM 56, RAM 58 acting asstorage means, and an output I/F 59 are built into the control part 50.A control program to be executed by the CPU 54, that is, a programcorresponding to a flowchart of FIG. 3 described below is stored in theROM 56, and the RAM 58 is formed so as to provide a working area to theCPU 54. When i_(da)=i_(d), i_(qa)=i_(q), θ_(re)=θ_(r), i_(ua)=i_(u),i_(va)=i_(v) are used in “Practice of theory and design of AC servosystem”, fourth edition, General electronic publishing company, writtenand edited by Hidehiko Sugimoto, page 79, expression (4.11), thefollowing expression is obtained. $\begin{matrix}{\begin{bmatrix}i_{d} \\i_{q}\end{bmatrix} = {{\sqrt{2}\begin{bmatrix}{{\sin\left( {\theta_{r} + {\pi/3}} \right)}\sin\quad\theta_{r}} \\{{\cos\left( {\theta_{r} + {\pi/3}} \right)}\cos\quad\theta_{r}}\end{bmatrix}}\quad\begin{bmatrix}i_{u} \\i_{v}\end{bmatrix}}} & (1)\end{matrix}$where i_(d): d-shaft armature current, i_(q): q-shaft armature current,θ_(r): magnetic pole position

The following expression is obtained from this expression (1).√{square root over (2)}{i _(u) sin(θ_(r)+π/3)+i _(v) sin θ_(r) }=i_(d)  (2)√{square root over (2)}{i _(u) cos(θ_(r)+π/3)+i _(v) cos θ_(r) }=i_(q)  (3)

The following expression is obtained from the expressions (2) and (3).i _(u) =i ₀·sin {θ_(r)−tan⁻¹(|i _(d) |/|i _(q)|)}  (4)i _(v) =i ₀·sin {θ_(r)−tan⁻¹(|i _(d) |/|i _(q)|)+4π/3}  (5)

Also, from i_(w)=−i_(u)−i_(v),i _(w) =i ₀·sin {θ_(r)−tan⁻¹(|i _(d) |/|i _(q)|)+2π/3}  (6)where i₀=−√{square root over (2/3)}(i_(d) ²+i_(q) ²)^(1/2)

In each phase current i_(u), i_(v), i_(w) flowing through the motor 3 ofthe expressions (4) to (6), at the normal time, from the viewpoint ofimproving efficiency of the motor 3, the motor 3 is driven andcontrolled with a d-shaft armature current i_(d) set to zero. Currentwaveforms of the phase currents i_(u), i_(v), i_(w) of the case ofsetting the d-shaft armature current i_(d) to zero are shown in FIG. 3.

After detecting that the motor 3 is locked, a magnetic pole positionθ_(r) of a rotor of the motor 3 is changed equivalently by changing[tan⁻¹(|i_(d)|/|i_(q)|)] in the expressions (4) to (6) by passing thed-shaft armature current I_(d) through the motor 3 while maintaining avalue of a q-shaft armature current I_(q) so that absolute values ofcurrents of two phases are larger than that of the other one phase amongthree phases whose the currents flow through the motor 3 becomesubstantially equal. As a result of this, the flow of a large currentthrough a particular phase is suppressed at the time of the lock of themotor 3.

However, the passage of the d-shaft armature current I_(d) through themotor 3 increases the maximum value i₀ of each the phase current i_(u),i_(v), i_(w) as is evident from the expressions (4) to (6), so thatthere is a need to pass the minimum necessary d-shaft armature currentI_(d).

Such a minimum necessary d-shaft armature current I_(d) is obtained asfollows. First, when the d-shaft armature current I_(d) to be passedthrough the motor 3 is grasped as a relation with the q-shaft armaturecurrent I_(q) and a current ratio is set to A, it can be expressed asA=|i_(d)|/|i_(q)|, so that the following expression holds.|i _(d) |=A|i _(q)|  (7)

When this expression (7) is substituted into the expression (4), thefollowing expression is obtained. $\begin{matrix}\begin{matrix}{i_{u}^{\prime} = {{- \sqrt{2/3}}\quad{{i_{q}\left( {A^{2} + 1} \right)}^{1/2} \cdot {\sin\left( {\theta_{r} - {\tan^{- 1}A}} \right)}}}} \\{= {B\quad{i_{q} \cdot {\sin\left( {\theta_{r} - {\tan^{- 1}A}} \right)}}}}\end{matrix} & (8)\end{matrix}$

In like manner, when the expression (7) is substituted into theexpressions (5) and (6), the following expressions are obtained.i _(v) ′=Bi _(q)·sin {(θ_(r)−tan⁻¹ A)+4π/3}  (9)i _(w) ′=Bi _(q)·sin {(θ_(r)−tan⁻¹ A)+2π/3}  (10)where B=−√{square root over (2/3)}(A²+1)^(1/2)

In the case that the motor 3 is in the lock state, the d-shaft armaturecurrent I_(d) is passed so as to shift the magnetic pole position θ_(r)equivalently so that two phase currents become equal in a direction ofdecreasing an absolute value of a current of a phase having the largestcurrent among each of the phase currents i_(u), i_(v), i_(w). Therefore,in FIG. 3, the following expression is obtained from the expressions (8)to (10) in order to shift the magnetic pole position θ_(r) of the motor3 to 0, π/3, 2π/3, π(3π/3), 4π/3, 5π/3 equivalently.(θ_(r)−tan⁻¹ A)=π·n/3  (11)where n: phase factor, any value of 0, 1, 2, 3, 4, 5

Here, in FIG. 3, in the case of locking in a magnetic pole positionθ_(a) of the rotor of the motor 3, 240° or 300° resides in the vicinityof the magnetic pole position θ_(a) to shift the magnetic pole positionθ_(r) equivalently so that two phase currents become equal. However, inthe case of shifting the magnetic pole position θ_(r) to 300°equivalently in a direction b in which an absolute value of a currentincreases, the d-shaft armature current i_(d) becomes large, so that itis constructed so as to shift the magnetic pole position θ_(r) to 240°equivalently in a direction a of decreasing an absolute value of acurrent of a phase.

Therefore, it is constructed so that the d-shaft armature current i_(d)to be passed through the motor 3 does not become large unduly by settingthe equivalent maximum shift angle of the magnetic pole position θ_(r)of the rotor to 30°.

From the expression (11), the current ratio A is shown as the followingexpression.A=tan(θ_(r) −π·n/3)  (12)

Here, in the case of locking when the magnetic pole position θ_(r) ofthe rotor is 0°<θ_(r)≦30°, 330°<θ_(r)≦360°, it is constructed so as tobe set to a phase factor n=0 and equivalently shift the magnetic polepositions θ_(r) (hereinafter called a phase) of the currents i_(u),i_(v) to 0.

Similarly, for 30°<θ_(r)≦90°, phases of the currents i_(u), i_(v) areshifted to π/3, so that it becomes the phase factor n=1, and for90°<θ_(r)≦150°, phases of the currents i_(u), i_(w) are shifted to 2π/3,so that it becomes the phase factor n=2.

Similarly, for 50°<θ_(r)≦210°, phases of the currents i_(w), i_(v) areshifted to π, so that it becomes the phase factor n=3, and for210°<θ_(r)≦270°, phases of the currents i_(u), i_(v) are shifted to4π/3, so that it becomes the phase factor n=4.

Similarly, for 270°<θ_(r)≦330°, phases of the currents i_(u), i_(w) areshifted to 5π/3, so that it becomes the phase factor n=5.

However, when the magnetic pole position θ_(r) of the rotor is 30°, 90°,150°, 210°, 270°, 330°, since currents flowing through two phases of themotor 3 are equal, there is no need to pass the d-shaft armature currentI_(d), so that it becomes the d-shaft armature current I_(d)=0.

On the other hand, torque T_(e) occurring in the motor 3 is shown as thefollowing expression when Φ_(fa)=Φ_(f), i_(qa)=i_(q) are used in page20, expression (2.23) of the above-mentioned literature.T_(e)=pΦ_(f)i_(q)  (13)where p: the number of pole pairs, Φ_(f): the number of armature windinglinkage magnetic fluxes (Wb)

From the expression (13), the torque does not change even in the case ofpassing the d-shaft armature current i_(d).

Here, for example, when it is assumed that it is locked in the case thatthe magnetic pole position θ_(r) of the rotor of the motor 3 is in therange of 240°<θ_(r) ≦270°, for example, the magnetic pole position θ_(r) is 260° (4.54 rad), the positive number n is obtained from theabove and the current ratio A is shown as the following expression fromthe expression (11).A=tan(4.54−4π/3)=0.38

Therefore, a U phase current i_(u)′ which passes the d-shaft armaturecurrent i_(d) is shown as the following expression from the expression(8).i _(u)′=−√{square root over (2/3)}i _(q)(0.38²+1)^(1/2)·sin(4π/3)i _(u)′=−√{square root over (2/3)}i _(q)·1.07·−0.866=0.75i _(q)

On the other hand, a U phase current i_(u) which does not pass thed-shaft armature current i_(d) is shown as the following expression bybeing set to the d-shaft armature current i_(d)=0 in the expression (4).$\begin{matrix}\begin{matrix}{i_{u} = {{- \sqrt{2/3}}\quad{i_{q} \cdot {\sin\left( {\theta_{r} - {\tan^{- 1}0}} \right)}}}} \\{= {{{- \sqrt{2/3}}\quad{i_{q} \cdot \sin}\quad 260^{\circ}} = {0.80\quad i_{q}}}}\end{matrix} & (14)\end{matrix}$

On the other hand, lives of the transistors T₁ to T₆ are proportional tothe biquadrate of a temperature rise ΔTj in junction parts of thetransistors T₁ to T₆, and the temperature rise ΔTj of each of thetransistors T₁ to T₆ is proportional to currents flowing through thetransistors T₁ to T₆.

In the case of locking in the magnetic pole position θ_(r) of the motor3, the life of the transistor T₁ with the largest current flowing amongthe transistors T₁ to T₆ is extended in proportion to the biquadrate ofa ratio K between the U phase current i_(u)′ of the case of passing thed-shaft armature current i_(d) and the U phase current i_(u) of the caseof setting the d-shaft armature current i_(d) to zero. When this isestimated by the above-mentioned example, the life of the transistor T₁is extended 1.31 times as described below.

 K=(i _(u) /i _(u)′)⁴=(0.80i _(q)/0.75i _(q))⁴=1.31

Incidentally, a current of each the phase current i_(v) increasesinversely by passing the d-shaft armature current i_(d), but a life ofonly a particular transistor among the transistors T₁ to T₆ is notshortened.

An action of the motor control system configured as described above willbe described by FIGS. 1 to 4. FIG. 4 is a flowchart showing an action ofthe motor control system shown in FIG. 1.

Now, when an operation start command is inputted to the control part 50,the CPU 54 detects this operation start command (step S101), and athree-phase AC voltage is applied to the motor 3 from the inverter part30, and the motor 3 is rotated as the d-shaft armature current i_(d)=0,and the movable metal mold 13 coupled to a ball screw 5 moves in theright direction to abut on the fixed metal mold 15 and the motor 3 islocked. The CPU 54 detects a rotational angle Θ of the motor 3 throughthe input I/F 52 by the encoder 40 acting as rotational angle detectionmeans and in the case of detecting that there is no change in therotational angle Θ by a predetermined angle for predetermined time (lockdetection means), it is decided that the motor 3 is locked and a lockdetection signal is generated (step S103), and the rotational angle Θ ofthe motor 3 of the encoder 40 is read, and the magnetic pole positionθ_(r) of the motor 3 is calculated and obtained by the number of polepairs of the angle Θ×the motor 3 (step S105).

The CPU 54 obtains n of the expression (8) from the magnetic poleposition θ_(r) (step S107), and obtains the current ratio A from A=tan(θ_(r)−π·n/3) as shown in the expression (12) (step S109), and obtainsthe d-shaft armature current I_(d) from I_(d)=AI_(q) as shown in theabove and also passes the d-shaft armature current I_(d) through themotor 3 from the inverter part 30. That is, it is controlled so as topass the d-shaft armature current i_(d) through the motor 3 so thatabsolute values of currents of two phases are larger than that of theother one phase among three phases whose the currents flow through themotor 3 are made substantially equal (step S111). As a result of this,even in the case that the motor 3 is in the lock state, a large currentdoes not flow through a particular phase of the motor 3 and currents ofparticular transistors T₁ to T₆ do not increase and a life of theinverter part 30 extends.

Industrial Applicability

As described above, a motor control system according to the presentinvention is suitable for use in, for example, a motor-driven injectionmolding machine.

1. A motor control system characterized by comprising: an inverter parthaving switching means for applying a three-phase AC voltage to a motor,lock detection means for detecting a lock state of the motor and alsogenerating a lock detection signal by the detection, and current controlmeans for increasing of decreasing a d-shaft armature current i_(d)through the motor while maintaining a q-shaft armature current constantso that an absolute value of a current of a phase with the largestcurrent flowing through the motor decreases based on the lock detectionsignal.
 2. A motor control system as defined in claim 1, characterizedin that the current control means passes a d-shaft armature currenti_(d) through the motor so that absolute values of currents of twophases are larger than that of the other one phase among three phaseswhose the currents flow through the motor are made substantially equal.3. A motor control system as defined in claim 1 or 2, characterized inthat the current control means satisfies the following A when it isassumed that a q-shaft armature current passed through the motor isI_(q) and a magnetic pole position of a rotor of the motor is θ_(r)I_(d)=AI_(q) where A=tan (θ_(r)−π·n/3) where n=0 for 0°<θ_(r)≦30°,330°<θ_(r)≦360°, n=1 for 30°<θ_(r)≦90°, n=2 for 90°<θ_(r)≦150°, n=3 for150°<θ_(r)≦210°, n=4 for 210°<θ_(r)≦270°, n=5 for 270°<θ_(r)≦330°.